Nucleotide sequence and predicted functions of the entire <i>Sinorhizobium meliloti</i> pSymA megaplasmidMelanie J. Barnett, Robert F. Fisher, Ted Jones et al.|Proceedings of the National Academy of Sciences|2001 The symbiotic nitrogen-fixing soil bacterium Sinorhizobium meliloti contains three replicons: pSymA, pSymB, and the chromosome. We report here the complete 1,354,226-nt sequence of pSymA. In addition to a large fraction of the genes known to be specifically involved in symbiosis, pSymA contains genes likely to be involved in nitrogen and carbon metabolism, transport, stress, and resistance responses, and other functions that give S. meliloti an advantage in its specialized niche.
Reduction of Adenosine-5′-Phosphosulfate Instead of 3′-Phosphoadenosine-5′-Phosphosulfate in Cysteine Biosynthesis by <i>Rhizobium meliloti</i> and Other Members of the Family <i>Rhizobiaceae</i>We have cloned and sequenced three genes from Rhizobium meliloti (Sinorhizobium meliloti) that are involved in sulfate activation for cysteine biosynthesis. Two of the genes display homology to the Escherichia coli cysDN genes, which code for an ATP sulfurylase (EC 2.7.7.4). The third gene has homology to the E. coli cysH gene, a 3'-phosphoadenosine-5'-phosphosulfate (PAPS) reductase (EC 1.8.99.4), but has greater homology to a set of genes found in Arabidopsis thaliana that encode an adenosine-5'-phosphosulfate (APS) reductase. In order to determine the specificity of the R. meliloti reductase, the R. meliloti cysH homolog was histidine tagged and purified, and its specificity was assayed in vitro. Like the A. thaliana reductases, the histidine-tagged R. meliloti cysH gene product appears to favor APS over PAPS as a substrate, with a Km for APS of 3 to 4 microM but a Km for PAPS of >100 microM. In order to determine whether this preference for APS is unique to R. meliloti among members of the family Rhizobiaceae or is more widespread, cell extracts from R. leguminosarum, Rhizobium sp. strain NGR234, Rhizobium fredii (Sinorhizobium fredii), and Agrobacterium tumefaciens were assayed for APS or PAPS reductase activity. Cell extracts from all four species also preferentially reduce APS over PAPS.